Spline forming machines using reciprocating racks are well known in the art as evidenced, for example, by the large number of patents owned by the assignee of the present application. These include: U.S. Pat. No. 4,712,410; U.S. Pat. No. 4,712,408; U.S. Pat. No. 4,689,980; U.S. Pat. No. 4,677,836; U.S. Pat. No. 4,506,537; U.S. Pat. No. 4,487,047; U.S. Pat. No. 4,467,631; U.S. Pat. No. 4,399,678; U.S. Pat. No. 4,380,918; U.S. Pat. No. 4,270,375; U.S. Pat. No. 4,729,233; U.S. Pat. No. 4,741,191; U.S. Pat. No. 4,756,179; U.S. Pat. No. 4,756,182; U.S. Pat. No. 4,819,468; U.S. Pat. No. 4,829,800; U.S. Pat. No. 4,852,375; U.S. Pat. No. 4,882,926; U.S. Pat. No. 4,891,962; U.S. Pat. No. 4,956,986; and, U.S. Pat. No. 5,509,287.
Most spline forming machines currently used in the United States are of the horizontal type, in which horizontally reciprocating forming tools are driven across a rotatable workpiece to form the splines. However, the manufacturing industry is increasingly implementing the "cell" concept in which machines are grouped closely, requiring more efficient use of floor space than the typical horizontal spline-forming machine offers. In Japan, where the cell concept is more widely established, it is known to use vertical rack spline-forming machines of the type shown in U.S. Pat. No. 4,646,549 to Saito et al.
Vertical rack spline-forming machines, however, tend to be more lightly built and less rigid than horizontal machines, adversely affecting the spline-forming operation in which powerful forces are generated between the racks and the workpiece. Saito et al., for example, uses narrow "slide columns" as vertical bases, with a direct sliding fit between the slides and the column faces requiring massive slab-like front and rear tie bars through which workfeeding and slide-synchronizing mechanisms must be routed. The Saito et al. columns further require a structural lower base and upper connecting frame to tie the columns together. Friction between the mating slide and column faces is inherently high, and the tie bar preloading on the slide columns likely affects the fit of the slides on the column faces, the force of the spline-forming dies on the workpiece, and therefore the quality of the forming operation.
The hydraulic drive systems on prior machines, especially vertical machines such as Saito et al. where the drive cylinders are on top of the machine, present maintenance difficulties such as keeping the machine clean and free from hydraulic leaks. Known hydraulic drives also take up floor space, generate significant noise with their associated pressure packages, and require timers to shut pressure down during periods of non-use to conserve energy.
Another difficulty with vertical rack spline-forming machines is encountered when trying to locate their slide linkages and timing gear compactly around the machine. The common drive and linkage operating the two sliding racks must be synchronized, and Saito et al. discloses several fairly complicated arrangements for doing so: timing racks connected to the spline-forming "flat dies", the timing racks meshing with a passive synchronizer or timing gear; a hydraulically-driven timing gear; motor-driven crank arms and connecting rods; and a hydraulic circuit activated by limit switch position sensors.
Another drawback of prior art machines is the need for a datum surface against which the reciprocating racks are calibrated during assembly so that each rack is evenly positioned relative to the workpiece. If either of the spline-forming racks loses its calibration and therefore its synchronicity with the other rack, it is often necessary to either regrind the datum surfaces, or to make a full-tooth adjustment to the out-of-sync rack.